Differential activation of respiratory muscles during wakefulness and sleep.

Evidence exists that strongly suggests that an imbalance in both the magnitude and timing of electrical activity between the upper airway and chest wall inspiratory muscles can exist during sleep. Too little or delayed activity of upper airway inspiratory muscles is associated with upper airway narrowing or collapse in patients with obstructive apnea. Preferential activation of upper airway muscles is associated with a decrease in upper airway resistance or in reopening of the airway following an apnea. These interrelationships between the upper and lower respiratory muscles may be exacerbated during the periodic breathing in sleep, thereby contributing to airway closure. This concept, in conjunction with those related to airway collapsibility and reflex control of upper airway caliber, should lead us closer to understanding the pathophysiology of obstructive sleep apnea.